1. Field of the Invention
The present invention relates to a radiation image detection apparatus, which is used in an X-ray imaging apparatus for medical use or the like, and a manufacturing method of the same.
2. Description of the Related Art
In recent years, a radiation image detection apparatus, such as a Flat Panel Detector (FPD), capable of directly converting radiation into digital data, has been put to practical use. The radiation image detection apparatus is being rapidly distributed since it has an advantage of being able to immediately verify an image compared to conventional image plates.
Various types of such radiation image detection apparatuses were proposed. For example, an indirect type converts radiation into light in a single operation using a scintillator of, for example, CsI:Tl, GOS (Gd2O2S:Tb), or the like, converts the converted light into electric charges through a semiconductor layer, and then stores the electric charges.
It is preferred to decrease the amount of radiation emitted when the radiation image detection apparatus is used, for example, in living bodies. In the field of optical detectors, the scintillator, which emits a great amount of light and has high sensitivity, is preferable. From that point of view, several radiation image detection apparatuses were proposed (e.g., Japanese Patent No. 3333278 and Japanese Patent Application Laid-Open (JP-A) No. 2001-330677). Such a radiation image detection apparatus is constructed by attaching a scintillator, made of crystals of CsI or the like, to an insulating substrate, and emits radiation from an optical detector side.
In the scintillator, which is configured to include such crystals, it is known in theory that sensitivity rises as according to the thickness of the crystals. In practice, however, if the thickness of the crystals is increased up to a certain value, light is attenuated or scattered while it is passing through the scintillator. This causes problems such as being unable to obtain sufficient sensitivity or blurring of an image. Therefore, additional improvement in sensitivity is required.
For the purpose of improving sensitivity, a radiation image detection apparatus was proposed, in which a scintillator layer is constructed with an assembly of columnar crystals, and which ensures that the density of an activator has a slope (e.g., JP-A No. 2008-51793). However, there is possibility that the scintillator may decrease the yield of an article due to the need for precision in process control during the manufacturing. In addition, neither sensitivity nor the resolution of a produced image is satisfactory, and improvement is still demanded.